The sizable damage bonus is applicable as long as the Hit Streak number is red, and the sword is glowing. Once the charge(s) are expended by performing a special move (such as an Execution or Wraith Blast), the bonus does not apply until the Hit Streak is charged again.

At mid to high Hit Streak levels (15+ and 30+ respectively), the damage from a single well-timed Flame of Vengeance-enhanced Critical Strike can slay normal Uruk in a single hit, and at high streaks will also shatter Defender shields and utterly bypass the Berserker's ability to Counter Talion. So when the streak is high and charged, it is often expedient to use chains of sword strikes to quickly kill large groups, instead of consuming the charge to perform an Execution.